1. Field of the Invention
The present invention relates to a group III–V compound semiconductor light-emitting device, and more particularly to improvement in light extraction efficiency in a light-emitting diode chip including a plurality of nitride-based semiconductor layers stacked on a transparent substrate.
2. Description of the Background Art
In general, nitride semiconductor light-emitting diode chips are manufactured by forming an epitaxial wafer having a plurality of nitride semiconductor layers including an emission layer which are stacked on a substrate and then dividing the wafer into a plurality of chips. For a conventional gallium nitride (GaN)-based semiconductor light-emitting diode chip, a substrate of sapphire or the like is generally used and a light-emitting diode device including such a chip is now commercially available.
In a light-emitting diode device with a sapphire substrate, since the substrate is insulative, it is difficult to form a structure in which a p-side electrode and an n-side electrode are provided on the upper and lower sides of the substrate, respectively, and thus it is necessary to extract light from the light-emitting diode chip through a transparent electrode. Furthermore, since the sapphire substrate has a high hardness, it is necessary to process the substrate into a thin film state and then divide the wafer into chips.
Commercially available typical nitride semiconductor light-emitting devices according to the prior art are provided by forming a GaN-based semiconductor stacked-layer structure on a sapphire substrate and reducing thickness of the substrate to approximately 100 μm and then dividing the structure into chips. As disclosed in Japanese Patent Laying-Open No. 2002-270962, for example, in the case of dividing a GaN-based semiconductor light-emitting device layer formed on a sapphire substrate, the substrate is processed to a 80 μm thickness. Japanese Patent Laying-Open No. 2000-068556 investigates a method of producing chips with a good yield rate from an epitaxial wafer including a plurality of nitride semiconductor layers stacked on a sapphire substrate, whereby the wafer having a thickness of 80 μm is divided into chips.
As understood from the above, in the conventional nitride semiconductor light-emitting diode chip, it is necessary to form a transparent electrode (typically under a p-side electrode) as well as p-side and n-side electrodes on a surface of the semiconductor stacked-layer structure included in the chip. The backside of its substrate is joined to a pedestal. Then, due to the p-side and n-side electrodes which block light, there occurs a loss in efficiency of extracting light from the chip towards the outside.
The high hardness of the sapphire substrate also causes difficulties in dicing or scribing to divide the epitaxial wafer including the sapphire substrate into a plurality of light-emitting diode chips with a good yield rate. Accordingly, after formation of the epitaxial wafer, the thickness of the substrate needs to be reduced to less than 100 μm by grinding the substrate, for example. However, the reduced thickness of the substrate decreases the efficiency of extracting light from the side surface of the substrate towards the outside. Because of these circumstances, the conventional nitride semiconductor light-emitting diode chip including the sapphire substrate suffers a great loss in extracting light from the chip towards the outside.